[Feature]: Adding XmlStarlet to cli tools.

### What is your idea or feature suggestion?

Addition of the `xmlstarlet` cli tool to the PHP container.

### Benefits

While the `jq`/`xq` tool set allows querying of `xml` & `json`.
`xmlstarlet` tops that with easier to use function to edit/manipulate those structures.
[Man pages](https://linux.die.net/man/1/xmlstarlet) outline the functions which are provided.
Together with `selection` there are also utilities to allow `edit`, `validate`, `transform`, `format` etc. an `xml` structure, which are either missing in `xq` or requiring a workaround to reproduce.

### Where can we find information about this?

[SourceForge](https://xmlstar.sourceforge.net/)
Can't quite verify the authenticity but there seems to be a github repo too [Github](https://github.com/fishjam/xmlstarlet)
I'd trust the SourceForge one if i had to choose.

### Are you willing to provide a PR to address this?

None